Muffler apparatus with filter trap and method of use

ABSTRACT

Muffler apparatus for reducing both sound and particulates from exhaust gases from an engine. The apparatus includes resonating chambers, flow distribution structure and a cellular ceramic core filter module. Filter regeneration mechanism includes a heating element for heating the carbon on the inlet end of the ceramic core to combustion temperature. Particulate ignition resulting in regeneration occurs when combustion air is provided; in alternate embodiments, combustion air first flows through a preheater system. A processor unit with particular logic controls the apparatus.

FIELD OF THE INVENTION

The invention is directed generally to muffler devices for vehicles,primarily vehicles powered by diesel engines. The muffler includes afilter trap for capturing particulates exhausting from the engine andprovides a regenerating mechanism for oxidizing the particulates andemitting them as a nonpolluting gas.

BACKGROUND OF THE INVENTION

Particulate emissions by diesel-engine vehicles became a subject ofgreat concern to both environmental regulators and the automotiveindustry during the late 1970's and early 1980's. The concern wasprompted by the low supply of oil and the introduction of diesel enginesin a greater number of models of passenger cars and light trucks. At thetime, it was thought to be a wide trend toward dieselization. Althoughdiesel engines are normally more expensive than gasoline engines, theyare also much more efficient and, hence, the value of the higherefficiency propelled their popularity during that period. The prospectof greatly increased numbers of diesel vehicles, especially in urbanareas, generated concern about the impact of diesel particulateemissions on ambient air quality. Diesel particulate material is easilyrespired, incorporates potentially mutagenic and carcinogenic chemicals,and strongly absorbs light leading to degraded visibility in some areas.In response to these concerns, regulations by various agencies werepromulgated.

In response to the need to reduce diesel particulate emissions, vehicleand engine manufacturers began to attempt to reduce the amount ofparticulate matter generated by the engine and/or to remove theparticulate matter from the exhaust gas. The latter approach is relevantto the present invention. The latter approach in general uses a deviceknown as a trap-oxidizer. A trap-oxidizer system generally includes atemperature resistant filter (the trap) from which particulates areperiodically burned off (oxidized), a process commonly known asregeneration. The traps must be regularly regenerated so as not tobecome excessively loaded and create an undesirable back pressurethereby decreasing engine efficiency. Since the particulate materialcaptured by the trap is mainly carbon and hydrocarbons, its chemicalenergy is high. Once ignited, it burns readily and releases a largeamount of heat.

Possible traps for capturing diesel particulate emissions primarilyinclude cellular ceramic elements (see U.S. Pat. No. 4,276,071) andcatalytic wire-mesh devices (see U.S. Pat. No. 3,499,269). The presentinvention uses cellular ceramic filter elements.

Trap-oxidizer regeneration systems can be divided into two major groupson the basis of control philosophy. One group is positive regenerationsystems; the other group is self-regeneration systems. Positiveregeneration systems are relevant to the present invention and haveincluded use of a fuel fed burner (see U.S. Pat. No. 4,167,852), use ofan electric heater (see U.S. Pat. Nos. 4,270,936; 4,276,066; 4,319,896;and British published application No. 2,134,407) and detuning techniqueswhich aim to raise the temperature of exhaust gas temperature atselected times (see U.S. Pat. Nos. 4,211,075 and 3,499,260). Selfgeneration systems are directed to the use of fuel-additives containingcatalytic metals or the use of catalytic treated traps to lower theignition temperature of the captured particulates.

Although, as indicated, there has been effort directed to reducing theemission of diesel particulates, a simple, reliable and efficient trapsystem has not been available. Prior art systems have tended to be anaggregation of items which when linked together theoretically aredirected to solving the problem. None of the known systems, however, aredirected to the total exhaust problem, that is, both muffling sound andmaking emissions environmentally acceptable.

SUMMARY OF THE INVENTION

The present invention is directed to a particulate filter module of atype for trapping diesel particulate emissions and a method ofmanufacturing the module. The invention is also directed tomuffler-filter apparatus which includes the module along with soundattenuating mechanism, as well as a method of using such muffler-filterapparatus.

The particulate filter module of the present invention includes aceramic filter element enclosed along a side region by a rigid housing.The housing has mechanism for longitudinally retaining the ceramicfilter element between opposite ends. The module also has mechanism forcushioning the filter element with respect to the rigid housing and forresisting heat transfer from the filter element to the housing, as wellas mechanism for sealing the cushioning mechanism between the filterelement and the housing at the opposite ends of the rigid housing insuch a way as to be partially compressed between the filter element andthe longitudinal retaining mechanism at the ends of the rigid housingwhich then also puts the ceramic core in axial preload.

The method for making the particulate filter module includes steps ofwrapping the side region of the ceramic filter element with anintumescent cushioning and heat resistant material, slipping the wrappedfilter element into a housing, placing sealing mechanism at ends of theheat resistant material, and forming inwardly turned ends on the housingto compress a portion of the sealing mechanism between the filterelement and the inwardly turned ends.

The present method may be of further advantage in certain cases toinclude steps of partially prerolling a metallic sheet before slippingthe wrapped ceramic filter into it and thereafter squeezing the rolledsheet to a predetermined cylindrical dimension and welding the seamthereof. It may be of still further advantage to heat the completedmodule before use to cure the intumescent and heat resistant material.

The module is particularly advantageous since it is modular and yetincludes many features important to proper use of a cellular ceramicelement. In the modular form, the element may be used in a particularhousing, removed for regeneration, and stored or installed in the sameor a different housing. Additionally, the modular concept leads tosimpler manufacture of larger assemblies, such as muffler apparatus.

The present ceramic filter module has intumescent, heat resistantmaterial about the ceramic element to transversely compress the ceramicelement and to contain the heat during regeneration of the element. Thematerial has a diagonal joint so that the seam is not a ready source ofleakage. Additionally, the heat resistant material is sealed in place atthe ends of the ceramic element.

Of further importance, the housing includes inwardly turned ends whichnot only compress the seal, but provide an axial, preloaded containmentfor the ceramic element. Thus, the heat resistant material transverselyloads and cushions the ceramic element with respect to side shock. Theends of the housing provide an axial load. Such construction minimizesceramic cracking, and if cracking occurs, resists crack continuation. Inthis regard, such construction also allows for different thermal growthof the ceramic element and the metallic housing by providing atransition for different movement of the ceramic element and themetallic housing during thermal cycling. Thus, the present constructionprovides the advantages of a module and also the advantages ofprotecting the ceramic element with respect to the environmentalconditions it experiences.

In this regard, the method of making the ceramic filter module considersthe fragile and brittle characteristics of the components and leads tominimizing defects in the final product. Of particular note is thesimultaneous curling of the ends of the housing and equal compressingthereby to the ends of the ceramic element.

The muffler-filter apparatus of the present invention reduces both soundand particulates from exhaust gases of an engine. The apparatus includesa housing within which there are both mechanism for attenuating soundand mechanism for filtering particulates. In this regard, there are alsomechanism for heating the inlet end of the filtering mechanism to obtaincombustion and therefore regeneration, as well as mechanism forcontrolling the heating mechanism.

Of particular advantage then with respect to the present invention isthe dual result of filtering particulate from and muffling the sound ofexhaust gases. Of further particular import is that the heatingmechanism functions to heat primarily by radiation, thus simplifying theheating sub-assembly.

The ceramic filter module is a preferred filtering device for theapparatus. In order to obtain a preferable distribution of particulatesradially with respect to the axis of the filter module, themuffler-filter apparatus advantageously includes deflecting mechanism todirect flow of the exhaust gases away from the center portion of thefilter module. In this way, during regeneration, heat in the center ofthe filter does not build excessively and is better distributed therebyfurther alleviating the possibility of cracking.

Various embodiments provide further advantages with respect to theheating sub-assembly. For example, one embodiment provides for a morerapid and uniform heating of the ceramic element face by blowing a lowflow of air across the heating element until the face reaches atemperature near the combustion temperature, then the further rise isachieved by radiation only. In this way there is time for temperatureacross the face to become uniform before combustion starts. Anotherembodiment provides for an injector to atomize diesel fuel or otherliquid combustible onto the heating element to create a flame which at areduced electrical power consumption creates a very hot heat sourcethereby rapidly heating the face of the heating element. A furtherembodiment provides a reflecting surface for back scatter radiation sothat most of the available heat is kept near the face of the filterelement.

Another distinct advantage of the present apparatus is the use in someembodiments of a resonating chamber to hold heat storage granules alongwith a preheating element for the purpose of preheating combustion airdirected therethrough during the regeneration of the ceramic filterelement.

Also, the present apparatus advantageously compares a ratio of abaseline differential pressure upstream from the ceramic element to adifferential pressure across the ceramic element. The ratio is comparedto a predetermined value to determine when sufficient loading is presentand regeneration should be started. In this way, exhaust temperature,pressure and flow of the engine have little influence on system control.

The method of using the present muffler-filter apparatus includes thesteps of comparing the indicated differential pressure ratio to apredetermined value, and if the comparison results in a triggeringrelationship, then a diverter valve is functioned to direct exhaustgases away from the flow path through the housing and the heatingmechanism is turned on. Although not necessary, air from an air sourcemay be directed at a low flow rate across the heating element toward theceramic core face as the face heats. At a core face temperaturedifferential below combustion temperature, the air is turned off. Afterfurther heating and when the core face reaches combustion temperature,combustion air at a high flow rate is directed into the ceramic coreelement. A timer is started so that at the end of a timed period,whereupon regeneration should be complete, the diverter valve is openedand the flow of combustion air is stopped. The heaters are turned offafter combustion starts and before it ends.

The present method of use is simple and does not require stepsunimportant to regeneration and reuse of the muffler-filter apparatus assoon as possible. In fact, in some cases, it may be possible to continueto direct exhaust gases through the muffler-filter apparatus duringregeneration, as long as sufficient combustion air is also present.

The present invention is thusly summarized, and many advantages of theinvention have been indicated. The invention and its advantages may bebetter understood, however, by reference to the drawings brieflydescribed hereinafter and the detailed description of a preferred andother embodiments following thereafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an exhaust system having a muffler-filterapparatus in parallel with a conventional muffler in accordance with thepresent invention;

FIG. 1A is an alternate embodiment of an exhaust system which includesmuffler-filter apparatus in parallel;

FIG. 2 is a cross-sectional view of muffler-filter apparatus inaccordance with the present invention and also schematically illustratesa control system for the apparatus;

FIG. 3 is a plan view of a heating element of a type which can be usedto heat the inlet face of a ceramic filter element in accordance withthe present invention;

FIG. 4 is a side view of the heating element of FIG. 3;

FIG. 5 is a perspective view, partially cut away, of a ceramic filtermodule in accordance with the present invention;

FIG. 6 illustrates the function of air being filtered with a ceramicfilter element of the type used in the present invention;

FIG. 7 is a cross-sectional detail view of a portion of the module ofFIG. 5;

FIGS. 8A-F illustrate a method of making the module of FIG. 5;

FIG. 9 is a side view in partial cross-section of an alternateembodiment of muffler-filter apparatus in accordance with the presentinvention;

FIG. 10 is another alternate embodiment of muffler-filter apparatus;

FIGS. 11A-B show a logic diagram for using an exhaust system inaccordance with the present invention;

FIG. 12 is still another alternate embodiment of the front or inletportion of muffler-filter apparatus; and

FIG. 13 is yet another alternate embodiment of the front portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals designateidentical or corresponding parts throughout the several views, and moreparticularly to FIG. 1, an exhaust system of the type which can carrydiesel particulate emissions as addressed by the present invention isdesignated generally by the numeral 20. Exhaust system 20 is illustratedto be in fluid communication with diesel engine 22 via line 24. Line 24leads to connecting pipe 25 which includes a split so that one line 27connects with valve 29 while the other leg 31 connects with valve 33.Valve 29 is connected via line 40 with muffler-filter apparatus 28 whichleads to one tail pipe 42. Valve 33 connects with line 38 leading tomuffler 35 and then a second tail pipe 42.

Valves 29 and 33 are preferably two-way conventional brake valvesmodified only in that leakage across the gate is necessary in the usualapplication, while in the present invention any leakage is eliminated.Considering valve 29, it typically includes a tubular portion 37 havingopposite ends for fitting into seats (not shown) in flanges 39 and 41.Tubular portion 37 is clamped between flanges 39 and 41 by a pluralityof nut and bolt combinations 43 which extend between the flanges. Valve29 includes a pivotable gate 45 connected by linkage 47 to an actuator49. Actuator 49 may be operated hydraulically, pneumatically, by vacuum,electrically, mechanically or by any other suitable means. Lines 51illustrate a connection to a control mechanism (not shown). The controlmechanism preferably provides for synchronization between valves 29 and33, although mechanical linkage may also serve that function.

A control logic for system 20 has valve 29 open and valve 33 closedduring normal operation so that exhaust gases flow from motor 22 throughline 24 and leg 27 of connecting pipe 25, and through valve 29 and line40 to muffler-filter apparatus 28 and then tail pipe 42. In this way,the sound due to the exhaust gases is attenuated and particulates areremoved. When it is sensed, as described in more detail hereinafter,that the filter of apparatus 28 should be regenerated, valve 29 isclosed and valve 33 is opened. In this way, the regeneration system ofapparatus 28 can function, while the sound of the exhaust gases ismuffled in muffler 35 by passing alternatively through leg 31 ofconnecting pipe 25 and then to valve 33 and line 38 for input to muffler35 and output at tail pipe 42. The concept of system 20 is that for mostof the system operational time, exhaust gases pass throughmuffler-filter apparatus 28 and are cleaned so as to exceed regulations.During the short regeneration time, the exhaust gases are not cleaned,although acceptable sound attenuation continues to occur. In any case,when the particulate level of total exhaust gases emitted from apparatus28 and muffler 35 is averaged, the particulate level exhausted is wellwithin regulations.

Alternate system 20A in FIG. 1A provides sound attenuation and filteringfunctions at all times. System 20A is illustrated to be in fluidcommunication with diesel engine 22 via line 24. Line 24 leads to adiverter valve 26 and muffler apparatuses 28 and 30 in parallel.Diverter valve 26 has a single inlet 32 with a pair of outlets 34 and36. Inlet 32 is in fluid communication through line 24 with engine 22.Outlet 34 is in fluid communication through line 38a with muffler-filterapparatus 28. Outlet 36 is in fluid communication through line 40a withmuffler-filter apparatus 30. Muffler-filter apparatuses 28 and 30 eachhave ceramic filter modules 90. Muffler-filter apparatuses 28 and 30also have tailpipes 42.

Valve 26 functions to divert exhaust gases from one muffler-filterapparatus to another so that when one filter module is beingregenerated, exhaust gases do not pass to atmosphere without beingfiltered, but rather must first pass through the filter module in theother muffler-filter apparatus. A typical diverter valve 26 as shown inFIG. 1A may be of a three way diverter type which includes a pivot arm44 controlled by a plunger arm 46 of a solenoid or air cylinder 48.Sealing disks 50 are attached to opposite sides of one end of pivot arm44 to mate with either seat 52 leading to outlet 34 or seat 54 leadingto outlet 36. Thus, with plunger arm 46 fully drawn into actuator 48,one of sealing disks 50 closes seat 54 and prevents exhaust emissionsfrom further flowing through muffler-filter apparatus 30. On the otherhand, with plunger arm 46 fully extended from solenoid 48, the other ofsealing disks 50 fits into seat 52 and opens exhaust gas flow tomuffler-filter apparatus 30 while closing exhaust gas flow tomuffler-filter apparatus 28. With plunger arm 46 midway between extremesof movement, sealing disks 50 close neither fluid communication path sothat emissions from engine 22 may exhaust partially through bothmuffler-filter apparatuses 28 and 30.

A typical muffler-filter apparatus, for example 28, in accordance withthe present invention is shown in more detail in FIG. 2. Apparatus 28includes housing 56 comprising a cylindrical wall 58 with opposite endwalls 60 and interior baffle members 62. Each of end walls 60 and bafflemembers 62 are formed to have an outer circular flange 64 to be fastenedto wall 58 along its interior and are also formed to have an innercircular flange 66 which forms an axially aligned opening. The wall 68extending between flanges 64 and 66 is preferably formed to have asymmetric curvature to provide appropriate structural strength. Walls 68of each pair of end walls 60 and baffle members curve convexly outwardlyfrom one another.

An inlet pipe 70 is attached to and held by flanges 66 of the right-mostpair of end wall 60 and baffle member 62. Pipe 70 is welded or otherwisefastened to be a part of line 38a which is in fluid communicationthrough valve 26 and line 24 with engine 22. Inlet pipe 70 is perforatedwith a plurality of first openings 72 in a region between end wall 60and baffle member 62 and is also perforated with a set of secondopenings 74 in a region between baffle wall 62 and the end 76 of inletpipe 70. A closure member 78 prevents fluid communication from end 76 ofinlet pipe 70. In this way, the chamber 80 formed between end wall 60and baffle member 62 functions acoustically as a resonating chambersince openings 72 allow exhaust gases to flow therethrough and bemuffled therein. Openings 74 allow exhaust gases to flow therethrough toa second chamber formed between baffle members 62 which functionsacoustically as an expansion chamber and wherein filter module 90 iscontained.

Similarly, an outlet pipe 82 is attached to and held by inner flanges 66of the left-most pair of end wall 60 and baffle member 62. Outlet pipe82 is fastened to exhaust tailpipe 42. Outlet pipe 82 includes aplurality of third openings 84 so that gases entering interior end 86may flow through openings 84 and be muffled within third chamber 88which then also functions acoustically as a resonating chamber, thirdchamber 88 being formed between end wall 60, baffle member 62 and outletpipe 82.

A ceramic filter module 90 is fastened to cylindrical wall 58 betweenthe interior ends 76 and 86 of inlet and outlet pipes 70 and 82 byfriction fit, weld, bracket or other known mechanism (not shown). Aheating element 92 is also attached in a known fashion to wall 58between interior end 76 of inlet pipe 70 and filter module 90, andpreferably in close proximity to the inlet end 94 of filter module 90 soas to heat the inlet end primarily by radiation. A temperature sensingdevice 96, such as a thermocouple, is located between heating element 92and inlet end 94 of module 90. Temperature sensing device 96 sensesfluid temperature in the region between heating element 92 and inlet end94 for a control purpose described more fully hereinafter. Likewise,tube 98 providing fluid communication for combustion air from outsidehousing 56 into chamber 80 and fittings 100, 101 and 102, located toopen into chamber 80 and located upstream and downstream from heatingelement 92 and filter module 90, but interior from resonating chambers80 and 88, respectively, are all needed for system control and areexplained more fully hereinafter.

It is noted that muffler-filter apparatus 28 includes reactiveattenuation chambers in the form of resonating chambers at opposite endsof the housing and an expansion chamber therebetween. The invention ischaracterized by at least one reactive attenuation element. Such term,of course, is recognized by those skilled in the art to include morethan expansion and resonating chambers. A reactive attenuation elementis anything designed to attenuate sound by phase cancellation due toreflection so that one wave cancels another by approaching the other.Reactive attenuation is contrasted with passive, absorptive attenuationwherein flow does not pass therethrough, but amplitude is neverthelessdamped thereby. Reactive attenuation is further contrasted withdissipated attenuation wherein sound is decreased, but not due to phasecancellation by interference.

Ceramic filter module 90 is shown more particularly in FIGS. 5-7. Module90 includes a cellular ceramic core 104 wrapped in a heat resistant,matted material 106 fitted within a metallic housing 108. The ends 110of housing 108 are bent inwardly to hold core 104 in a significant axialcompression, and a sealing material 112 provides a gasketing functionbetween ends 110 and core 104 and a sealing function with respect tointumescent, heat resistant material 106.

As indicated, the filtration mechanism comprises ceramic core 104. Core104 is an extruded ceramic which is fired so that the primarycrystalline compound is preferably cordierite. Such component iscommercially available for example from Industrial Ceramics Department,Ceramic Products Division, Corning Glass Works, Corning, N.Y. 14830. Inaddition, it is noted that the art of making ceramic filter materials isknown, e.g., see U.S. Pat. Nos. 4,340,403; 4,329,162; and 4,324,572. Thegeometry of core 104 is illustrated in FIG. 6. Square shaped cells 114are formed as parallel channels running the full length of the part. Thewalls 116 of channels 114 are porous , which allows them to be used asfilter media. Opposite ends of adjacent channels are plugged with aceramic material 118. This forces exhaust gases 120 through walls 116 sothat soot is collected on the walls as the gases pass therethrough. Theadvantage of this type of construction is that high filtration area isavailable in a small volume.

Heat resistant material 106 provides both an intumescent, cushioningfunction for core 104 and a fireretardant, heat resisting barrierbetween core 104 and rigid housing 108. Material 106 is preferably cutat an angle with respect to a longitudinal axial plane so that matingends 122 fit one over the other so as to eliminate a longitudinal slotand longitudinal leakage and the formation of a hot spot on housing 108therealong. The ends 122 of material 106 are held together until placedwithin housing 108 by a plurality of strips of tape 124 or otherequivalent fastening mechanism. A material 106 in sheet form is ratherelastic below temperatures on the order of 100° C. Material 106 thenprovides a cushioning function. As material 106 heats to 100° C. or soand above, it intumesces as allowed and becomes a substantially rigidthermal insulator. At all temperatures, material 106 provides a sealagainst vapors, smokes and water. Thus, exhaust gases are prevented fromexiting along the sidewall of core 104 and are directed through core 104from the inlet end to the other. The art of making such material is wellknown, e.g., see U.S. Pat. No. 4,273,879. A representative material 106is commercially available, for example, from Ceramic MaterialsDepartment, 3M Center, St. Paul, Minn. 55144.

As indicated, material 106 provides a cushioning function for ceramicelement 104. Before heating, material 106 holds together as a fibroussheet and is rather elastic. After heating, the binder in material 106has burned off so that the remainder is fibrous and granular-like.Unless contained, material 106 in the cured state would fall apart.Nevertheless, when contained, material 106 transversely compresses core104 so that in combination with the axial compression exerted by housing108, core 104 is securely confined in a fashion to resist cracking orbreakage due to normal use environmental conditions.

As indicated, material 106 is wrapped about the side region of core 104.In this configuration, material 106 has longitudinally opposite ends.The opposite ends are spaced from the inwardly turned ends 110 ofhousing 108. This creates a pair of circular grooves 128 between thecore filter element 104 and housing 108 between the ends 130 of material106 and the inwardly turned ends 110 of housing 108. The sealingmaterial is fitted within grooves 128. The sealing material ispreferably a compressible braided rope of fiberglass. In this way,material 112 may be placed in grooves 128 during the manufacturingprocess and appropriately deformed to function as a gasket between core104 and ends 110 of housing 108 and to function as a seal for material106.

Housing 108 is metallic, preferably an aluminized steel or a stainlesssteel, of about 18 gauge thickness. The corners of the flat sheet whichis formed to become housing 108 are notched so that when ends 110 areformed, the material formed is mainly the overlap layer in the seamarea. The edges are welded together.

The method of making module 90 is illustrated in FIGS. 8A-8F. A cellularceramic filter core 104 is shown in FIG. 8A. Core 104 is cylindrical.The matted heat resistant and intumescent cushioning material 106 iswrapped about core 104 as illustrated in FIG. 8B. Matted material 106has a set of facing ends 122 cut diagonally with respect to alongitudinally axial plane of core 104. The facing ends mate with oneanother. When facing ends 122 are brought into contact with one another,they are retained with strips of tape 124 or other equivalent fasteningmechanism. As shown in FIG. 8C, the wrapped core is then slipped into aprerolled metallic sheet 132 which will be further formed to becomehousing 108. With wrapped core 104 in place, prerolled sheet 132 isfurther squeezed or formed to a predetermined cylindrical dimension (seeFIG. 8D). As shown in FIG. 8E, material 106 longitudinally does notextend to end 126 of core 104, while rolled sheet 132 extends beyond end126. Thus, groove 128 is formed. A similar groove is formed at the otherend. Sealing rope 112 is placed into grooves 128 at the ends of material106. Finally, as shown in FIG. 8F, ends 110 of metallic sheet 132 aresimultaneously curled inwardly as forming dies 134 are moved together.Dies 134 are moved toward one another with sufficient force (20,000pounds or so) to curl not only ends 110, but also to put core 104 insignificant axial compression. The facing edges of sheet 132 are weldedtogether to form housing 108. Thus, core 104 is rigidly retained notonly at its ends, but also by the snugly fitting material 106 held bycylindrically rigid housing 108. Although not always necessary beforeuse, it is preferable as a final step in making module 90 to heat module90 above 100° C. so that the binder in material 106 is burned off andmaterial 106 uniformly intumesces.

Module 90, as described, or equivalent is attached within housing 56 ofmuffler-filter apparatus 28 between ends 76 and 86 of inlet and outletpipes 70 and 82, respectively. Alternately, module 90 may be removablyinstalled in housing 56 as indicated with respect to muffler-filterapparatus 30 in FIG. 1. A cylindrical clamp or other removable fasteningmechanism 136 attaches end sections 138 and 140 of housing 56a together.

Heating element 92 which is located in close proximity with inlet end 94of ceramic filter element 90 preferably provides a substantial amount ofradiant heat energy directed toward end 94. In this regard, heatingelement 92 may be a metallic, electrically resistive element.Alternatively, a heating element 92', as shown in FIGS. 3 and 4, may bean electrically resistive element 142 embedded in a ceramic casting 144.In this regard, it is noted that with respect to alternate embodiments,parts which are the same as the preferred embodiment are denoted withprimed numerals, while different parts are given new numerals.

Ceramic casting 144 is formed to include a plurality of rings of aplurality of openings 146 on both sides of the multi-ring heatingelement 142. Element 142 includes a pair of substantially parallel leads148 which are also parallel to a radial line of disk-shaped casting 144.Openings 150 are formed between leads 148 and lead to a plurality ofopenings 152 at the center of casting 144. A sufficient number ofvarious openings in casting 144 must be provided so that heating element92' does not become a significant restriction with respect to exhaustgases flowing through muffler-filter apparatus 28.

As exhaust emission gases from engine 22 flow through muffler-filterapparatus 28, the gases first flow into inlet pipe 70 for soundattenuation at resonating chamber 80. Gases continue to flow throughinlet pipe 70 to perforations 74. Gases are prevented from flowingdirectly through the outlet end of inlet pipe 70 by closure member 78.Consequently, gases flow from perforations 74 outwardly away from thecentral portion of housing 56. In this way, the greater flow of exhaustgases pass through the outer openings or spaces of heating element 92 or92' and into an outer ring of cellular core 104. A greater concentrationof particulates is thus formed in such outer ring. Such concentration ofparticulates in the outer ring is advantageous during regeneration ofthe ceramic core since heat does not then become concentrated at thecenter of core 104, but rather is more evenly distributed and evenpossibly somewhat more intense in the outer ring. Such flow leads to aheat distribution which may be dissipated in a way which minimizessignificant uneven expansion or contraction and any resultant cracking.Closure member 78 accomplishes the indicated function as a part of inletpipe 70 and alleviates any necessity for special flow directingstructure adjacent to core 104.

Since module 90 is attached to housing 56 in a way which prevents gasesfrom leaking past it without being filtered by it, gases pass throughceramic core 104 for entry to outlet pipe 82. While passing throughoutlet pipe 82, sound is attenuated further at the expansion chamberbetween baffles 62 and at resonating chamber 88.

Over time, filter module 90 traps a great enough quantity ofparticulates so as to begin to form a pressure restriction ofsignificance. When this occurs, module 90 must be regenerated. Themethod of regeneration is illustrated by the logic diagram of FIGS. 11Aand 11B. As the diagram indicates, the logic begins at "start" box 154and leads via line 156 to step 158 of reading the base line differentialpressure. With reference to FIG. 2, base line differential pressure isobtained with pressure transducers 159 and 160 attached to fittings 100and 101. Signals representing the pressure values are sent via lines 161and 162 to a processing unit 164. As further shown in FIG. 2, baselinepressure differential is the pressure differential across inlet pipe 70by the exhaust flow through perforations 72 and 74 upstream from heatingelement 92 and filter module 90.

Next, the logic diagram leads via line 166 to step 168 of reading trapdifferential pressure. Trap differential pressure is obtained withpressure transducers 160 and 170 attached to fittings 101 and 102 whichsend signals corresponding to the pressure read via lines 162 and 172 toprocessing unit 164. Trap differential pressure is read across filtermodule 90 and upstream from outlet pipe 82.

Next, the logic diagram shows line 174 leading to step 176 ofcalculating the ratio of baseline differential pressure to trapdifferential pressure. Then, via line 178 leading to step 180, the ratiois compared to a limit value. If the ratio is less than the limit value,then as line 182 shows, the logic is restarted and the pressures arereread and compared as indicated.

Line A--A divides the logic related to determining when regeneration isneeded from logic related to actual regeneration. If the ratio isgreater than the limit value, then as line 184 indicates leading to step186, the core temperature or a temperature between core 104 and heatingelement 92 is determined and compared to a predetermined low limittemperature. This is necessary to make certain that regeneration doesnot occur when the engine is not running. The temperature is measured bythermocouple or sensing device 96 and sent via line 192 to the processorunit 164. If the temperature is below the limit value, as logic line 188indicates, the temperature will be resampled. When the core temperatureis found to be above the limit value, then logic line 190 leads to step192 of closing the diverter valve. In the case of system 20, valve 29would be closed and valve 33 opened. In the case of system 20a, divertervalve 26 would be closed with respect to the particular muffler-filterapparatus to be regenerated.

The logic diagram then shows line 194 leading to parallel steps 196 and198 which occur preferably at about the same time. Step 196 showsheating element 92 being turned on. Step 198 shows a low flow of airfrom source 210 being initiated. The low level flow rate is preferablyless than half the flow rate of combustion air. The function of the lowflow of air is to aid in moving warmed air around heating element 92 tothe face of core 104, thereby better utilizing the heat and also topartially warm a depth beyond the face of core 104 by moving some warmair thereinto. It is noted, however, that step 198 is not needed foreffective regeneration.

With air on and the core heating, as shown by lines 200 and 202 leadingto step 204, temperature is again sensed and compared to a predeterminedtemperature which is less than the carbon particulate combustiontemperature. If the predetermined temperature has not been reached, thenas line 206 shows, temperature sensing continues. Once the predeterminedtemperature is sensed, as line 208 leading to step 210 indicates, thelow flow of air is turned off.

It is pointed out that the reduced air flow during warm-up of core 104assures sufficient core temperature to a sufficient depth to prevent aquench condition for the flame when combustion occurs.

The logic diagram then shows line 214 leading through circle B (whichshows where FIGS. 11A and 11B connect) to step 216 wherein thetemperature sensed by thermocouple 96 is compared to the knowncombustion temperature of diesel particulates. As indicatedhereinbefore, it is understood that the temperature sensed bythermocouple 96 could be the temperature of heating element 92, thetemperature of the inlet end 94 of ceramic element 104 or thetemperature of the gaseous fluid therebetween. If the temperature isless than the combustion temperature, then as shown by line 217temperature continues to be sensed. When the sensed temperature is foundto have reached the combustion temperature, then as shown by line 218leading to step 219 the air compressor 209 or other air source is turnedon so that air may flow through line 212 to inlet tube 98. Thecombustion air from source 209 enters muffler apparatus 28 via line 215and tube 98 at resonating chamber 80 and flows in perforated openings 72and out perforated openings 74 to heating element 92 and finally filtercore 104. With the temperature high enough and combustion air present,the particulates ignite and begin burning along a flame surface module90. It is noted that compressor or source 209 is controlled byprocessing unit 164 via line 211.

As shown by logic line 220 leading to step 211, internal regenerationtimer 222 is preferably started at the same time or shortly afterthermocouple 96 senses ignition temperature. Timer 222 is in electricalcommunication with processor unit 164 via lines 224 and 226 as shown onFIG. 2. As indicated in the logic diagram, line 223 leads to step 225wherein the heating element is turned off some time after combustion airis turned on. Then as shown by line 227 leading to step 228, thediverter valve is opened and the air compressor or source 209 is turnedoff after the timer times out. It is noted that the time period of timer222 is sufficiently long to allow complete burning of the particulatesin core 104 and, therefore, complete regeneration of core 104, or untilsufficient soot is removed to permit safe operation of engine flows.

Line C--C divides the regeneration logic from logic related toregenerating multiple units and/or resetting the just regenerated unit.As shown by logic line 242 leading to decision step 244, the logicsequence is returned via line 246 to start step 154 if the exhaustsystem has only a single muffler apparatus with a bypass muffler. Asshown by logic line 248 leading to step 250, the logic sequence iscycled for a second core, if such is present, as in system 20a of FIG.1A.

It is noted that alternate embodiments as shown in FIGS. 9 and 10include a combustion air preheating system 254 (FIG. 9) or 254" (FIG.10). Preheating system 254 is formed in resonating chamber 80'.Preheating system 254 includes a cylindrical wall 256 concentric withinlet pipe 70' and cylindrical wall 58' of housing 56'. Wall 256 isperforated with openings 258 so that combustion air from inlet tube 98'entering the outer annular space may diffuse through openings 258 alongthe longitudinal and circumferential extent of wall 256. A heatingelement 260 formed as a double helix is attached to end 60' and fitsabout midway between inlet pipe 70' and cylindrical wall 256. The spacewithin resonating chamber 80' between inlet pipe 70' and cylindricalwall 256 is filled with a granular, nonmetallic, gravel or ceramicpellet or bead or ball, etc., 262 so as to function as a heat storagebed. Preferably, the granular material 262 has a specific heat greaterthan the surrounding metal, for example, about 0.2 BTU/LB ° F. In thisway, heating element 260 heats the granular material, and the combustionair diffuses through it and is substantially heated thereby beforeflowing into and out of inlet pipe 70' and through heating element 92'to core 104'.

Alternately, as shown in FIG. 10, preheating system 254" may be formedsuch that granular material 262" completely fills resonating chamber80". Heating element 260" is preferably a double helix, but larger thanthe element of FIG. 9 so that it is located approximately half waybetween inlet pipe 70" and cylindrical wall 58". In this configuration,end 60" is perforated with openings 264. A flat, radial wall 266 isinstalled outwardly of end 60" so that a small diffusion chamber isformed in an annular, approximately triangular cross-sectional spacesurrounding inlet pipe 70". Inlet tube 98" is attached to flat outerwall 266 and opens into the annular diffusion space. In this embodiment,combustion air flows in inlet tube 98" to the diffusion space andthrough perforations 264 to resonating chamber 80". The air is heated asit continues to diffuse through the granulated material 262" pastheating element 260" to inlet pipe 70" whereafter the air flows asadequately described hereinbefore.

Preheating systems 254 or 254" are preferably connected with (not shown)and controlled by processor unit 164 and are turned on prior to closingthe exhaust diverter valve at step 192 and are left on for apredetermine variable time. The idea is that the granular material 262is allowed to be heated and store the heat before air is passedtherethrough for warming. The heating of the granular material can occurwhile exhaust gases are still passing through the muffler-filterapparatus.

Alternate inlet ends for a muffler-filter apparatus are shown in FIGS.12 and 13. With respect to this alternate embodiment, equivalentelements with the preferred embodiment are designated by the samenumeral along with the letter "b" for FIG. 12 and the letter "c" forFIG. 13. Housing 56b includes an end wall 60b and an interior bafflemember 62b to form a chamber 80b therebetween. Inlet pipe 70b isattached to and held by flanges 66b . Inlet pipe 70b is not perforatedto allow fluid communication with chamber 80b but is perforateddownstream from baffle member 62b as shown by opening 74b. As with thepreferred embodiment, housing 56b contains a ceramic module 90b and aheating element 92b for heating the carbon on the face of core 104b ofmodule 90b. Embodiment 28b is distinguished from the other embodimentsby the closure for inlet pipe 70b and the directing of combustion air tomodule 90b. In this regard, tube 98b leads from a source (not shown) tochamber 80b. A plurality of tubes 270 extend from baffle 62b to anenclosure 272. Tubes 270 provide fluid communication between chamber 80band enclosure 272, as well as help support enclosure 272. Enclosure 272has a side 274 away from module 90b which forms the closure member forinlet pipe 70b. Faced away from side 274 by a wall 276 is a perforatedside 278. Enclosure 272 is formed so that wall 276 is spaced somewhatfrom wall 58b of housing 56b. The gap allows for the flow of exhaustgases from inlet pipe 70b and perforations 74b to bypass enclosure 272and flow toward module 90b. Combustion air flows in tube 98b to chamber80b which functions as a manifold for the plurality of tubes 270. Airflows through tubes 270 to enclosure 272 and then out the preferablyuniformly distributed openings of perforated side 278 so as to provide auniform flow toward module 90b.

Embodiment 28c is the same as the preferred embodiment, except amechanism for atomizing a combustible, preferably diesel fuel, andinjecting it onto heating element 92c is shown. When the combustibleignites, a very hot heat source is provided and the face of module 90cmay be warmed more quickly. In this way, less electrical power is neededfor the heating with element 92c.

An atomizing element 280 is fastened as required to closure member 78c.Appropriate atomizing elements are known to those skilled in the art.Both air and fuel are provided to the atomizing element. This can bedone in a number of ways. As shown in FIG. 13, an air line 282 isconnected through a normally closed, two-way, two-position solenoidvalve 284 to a mixing chamber 286 via a line 288. Similarly, acombustible, like diesel fuel, is directed through a line 290 to anormally closed, two-way, two-position, solenoid valve 292 and then tomixing chamber 286 via line 294. From mixing chamber 286, the mixture isdirected via lines 296 and 298 through another normally closed, two-way,two-position, solenoid valve 300 to atomizing element 280.

Thus, the present exhaust system 20 may be embodied in a variety ofalternatives. The heart of the system, however, is a ceramic filterelement module in conjunction with a muffling mechanism and mechanismfor regenerating the filter element. Although the various embodimentshave been described in detail and the advantages of structure andfunction set forth, it is understood that other equivalents may bepossible as well. Therefore, it is finally understood that any changesmade in structure with respect to the disclosed embodiments, especiallyin matters of shape, size and arrangement, to the full extent extendedby the general meaning of the terms in which the appended claims areexpressed, are also within the principle of the present invention.

What is claimed is:
 1. A method for removing oxidizable particulatesfrom a filter trap in a muffler apparatus, said muffler apparatusincluding a housing having an inlet, an outlet, and a fluid flow passagefor exhaust gases leading from said inlet upstream to said outletdownstream, said fluid flow passage including a reactive acousticelement, said muffler apparatus also including in said fluid flowpassage means for filtering the particulates from the exhaust gases,said muffler apparatus still further including means for heating aninlet end of said filtering means and means for blowing air through saidheating means toward the inlet end of said filtering means, said mufflerapparatus yet further including valve means for controlling the flow ofexhaust gases to said housing, said muffler apparatus also includingfirst means for sensing a first pressure differential upstream of saidfiltering means and a second pressure differential across said filteringmeans and first means for comparing said first and second pressuredifferentials to a predetermined value to identify a first triggeringrelationship, said particulates having a combustion temperature, saidmuffler apparatus also including a second means for sensing one oftemperature of said heating means, temperature of fluid between saidheating means and said filtering means and temperature of said filteringmeans inlet end, second means for comparing said temperature relative toa predetermined temperature less than the combustion temperature toidentify a second triggering relationship, and third means for comparingsaid temperature relative to the combustion temperature to identify athird triggering relationship, said muffler apparatus also includingmeans for timing a predetermined period, said method comprising thesteps of:identifying the first triggering relationship; closing withsaid valve means flow of exhaust gases to said housing after said firsttriggering relationship; turning on said heating means after said valvemeans closing step; starting said air blowing means after said valvemeans closing step; identifying said second triggering relationship;stopping said air blowing means after said second triggeringrelationship; identifying said third triggering relationship; startingsaid air blowing means after said third triggering relationship;starting said timing means after said third triggering relationship;stopping said heating means during the timing of said timing means;stopping said air blowing means after said timed period; and openingwith said valve means flow of exhaust gasses to said housing after saidtimed period.
 2. The method in accordance with claim 1 wherein saidfirst step starting said air blowing means starts said air blowing meansat a reduced flow and said second step starting aid air blowing meansstarts said air blowing means at a significantly increased flow.
 3. Aparticulate filter module, comprising:a ceramic filter element havingopposite ends and a longitudinal side region therebetween; a rigidhousing having a wall enclosing said side region of said filter element,said wall being formed so as to leave a space between it and said sideregion, said wall having inwardly turned ends to longitudinally compresssaid filter element; means, within said space, for intumescing so thatsaid ceramic filter element is held in transverse compression by said;wall and means for sealing said intumescing means in said space betweensaid filter element and said wall.
 4. Muffler apparatus for reducingboth sound and particulates from exhaust gases from an engine,comprising:a housing having an inlet, an outlet, and a fluid flow pathleading from said inlet upstream to said outlet downstream; a reactiveocoustic element within said housing along said fluid flow path, saidelement attenuating the sound of said exhaust gases; means, within saidhousing along said fluid flow path, for filtering the particulates fromsaid exhaust gases, said filtering means including a ceramic filterelement having an inlet end; means for regenerating said ceramic filterelement; and means for controlling said regenerating means.
 5. Apparatusin accordance with claim 4 wherein said regenerating means includesmeans for primarily radiantly heating the inlet end of said filterelement.
 6. Apparatus in accordance with claim 5 wherein saidregenerating means also includes means for blowing combustion airthrough said heating means toward the inlet end of said filter element.7. Apparatus in accordance with claim 6 including means, within saidhousing, for preheating said combustion air upstream from said heatingmeans.
 8. Apparatus in accordance with claim 7 wherein said housinginlet includes a pipe with a downstream end and a plurality of openingsupstream from said downstream end, said apparatus further including achamber within said housing and about said inlet pipe, one of saidopenings providing fluid communication between said pipe and saidchamber, said combustion air blowing means including means for inlettingcombustion air into said chamber, said preheating means being withinsaid chamber.
 9. Apparatus in accordance with claim 8 wherein saidpreheating means includes a heating element and said chamber includes agranular material between said pipe and said heating element, saidgranular material storing heat from said heating element and requiringthe combustion air to diffuse therethrough to be heated thereby. 10.Apparatus in accordance with claim 9 wherein said combustion air blowingmeans includes an air source and wherein said combustion air inlettingmeans includes a wall having a plurality of openings thereindistributing combustion air from said source into said granularmaterial.
 11. Apparatus in accordance with claim 6 wherein said housingincludes a baffle separating said housing into adjacent chambers, saidcontrolling means including first means for sensing a first pressuredifferential across said baffle and a second pressure differentialacross said ceramic filter element, said controlling means alsoincluding first means for comparing said first and second pressuredifferentials relative to a predetermined value to identify a firsttriggering relationship, said controlling means also including firstmeans for starting said heating means when said first comparing meanshas identified said first triggering relationship.
 12. Apparatus inaccordance with claim 11 wherein said controlling means includes secondmeans for starting said air blowing means.
 13. Apparatus in accordancewith claim 12 wherein said controlling means includes second means forsensing one of temperature of said heating means, temperature of fluidbetween said heating means and said ceramic filter element, andtemperature of said ceramic filter inlet end, said particulates having acombustion temperature and said controlling means further includingsecond means for comparing said one temperature relative to apredetermined temperature less than the combustion temperature toidentify a second triggering relationship, said controlling means stillfurther including first means for stopping said air blowing means whensaid second comparing means has identified said second triggeringrelationship.
 14. Apparatus in accordance with claim 13 wherein saidcontrolling means further includes third means for comparing said onetemperature relative to said combustion temperature to identify a thirdtriggering relationship, said controlling means also including thirdmeans for starting said air blowing means after said third comparingmeans has identified said third triggering relationship, saidcontrolling means also including means for timing a predetermined periodbeginning after said third comparing means has identified said thirdtriggering relationship, said controlling means further including secondmeans for stopping said air blowing means at the end of said period. 15.Apparatus in accordance with claim 5 wherein said heating means includesan electrical heating element embedded in a ceramic plate, said ceramicplate having an opening therein to pass exhaust gases therethrough. 16.Apparatus in accordance with claim 4 wherein said ceramic filter elementis cylindrical and has a central portion at said inlet end including andsurrounding the axis, said apparatus further including means, withinsaid housing along said fluid flow path, for deflecting exhaust gasesoutwardly away from said central portion, thereby forming a ring outsidesaid central portion having a greater concentration of particulates,said housing inlet including a pipe with a downstream end, said pipeincluding a plurality of openings upstream from said downstream end,said deflecting means including an end cap fastened to said pipe at saiddownstream end to prevent fluid flow from said end thereby requiringfluid entering said pipe to exit through said openings.
 17. Apparatus inaccordance with claim 4 wherein said controlling means include valvemeans for selectively directing said exhaust gases one of through saidhousing and away from said housing, said controlling means includingmeans for sensing a first pressure differential upstream from saidceramic filter element and a second pressure differential across saidceramic filter element, said controlling means also including means forcomparing said first and second pressure differentials relative to apredetermined value to identify a triggering relationship, saidcontrolling means further including means for shifting said valve meansfrom directing said exhaust gases through said housing to directing saidexhaust gases away from said housing when said comparing means hasidentified said triggering relationship.
 18. Apparatus in accordancewith claim 17 wherein said valve means includes a two-way, two positionvalve.
 19. Apparatus in accordance with claim 17 wherein said valvemeans includes a three-way, three position valve.
 20. Muffler apparatusfor filtering particulates from exhaust gases from an engine,comprising:a housing having means upstream for inletting said exhaustgases and means downstream for outletting said exhaust gases, saidhousing including spaced-apart ends and a wall enclosing an interiorspace extending between said ends, said housing also including a baffleattached to said wall to divide said interior space into first andsecond chambers, said inletting means including an inlet pipe passingthrough and supported by one of said ends and said baffle, said inletpipe having inlet and outlet ends and an interior therebetween, saidinlet pipe further having first perforations to provide fluidcommunication between the interior of said inlet pipe and said firstchamber and second perforations to provide fluid communication betweenthe interior of said inlet pipe and said second chamber, said inlet pipealso having valve means for controllably closing said inlet end and aclosure member closing said outlet end so as to direct fluid from theinterior of said inlet pipe outwardly through said second perforations;a ceramic filter element mounted in said housing, said ceradic filterelement having an inlet end and an outer surface, said outer surfacebeing sealed with respect to the wall of said housing so as to forcefluid to pass through said ceramic filter element; means, mounted insaid housing, for heating a portion of said ceramic filter element;means for blowing air into said first chamber so that the air must flowthrough said first perforations into the interior of said inlet pipebefore being directed outwardly through said second perforations andpast said heating means to said ceramic filter element; and means forcontrolling said valve means, said heating means and said air blowingmeans, said controlling means including first means for sensing a firstpressure differential upstream from said ceradic filter element and asecond pressure differential across said ceramic filter element, saidcontrolling means also including first means for comparing a ratio ofsaid first and second pressure differentials relative to a predeterminedvalue to identify a first triggering relationship, said controllingmeans also including means for shifting said inlet pipe valve meansclosed after said first comparing means has identified said firsttriggering relationship, said controlling means further including meansfor starting said heating means after said first comparing means hasidentified said first triggering relationship, said controlling meansstill further inducing second means for sensing one of temperature ofsecond heating means, temperature of fluid between said heating meansand said ceramic filter element, and temperature of said ceramic filterinlet end, said controlling means also having second means for comparingsaid temperature relative to a predetermined combustion temperature toidentify a second triggering relationship, said controlling means alsoincluding means for starting and means for stopping said air blowingmeans at times between said first and second triggering relationships,said controlling means further including means for timing apredetermined period after said second triggering relationship and ameans for stopping said heating means and said air blowing by the end ofsaid period, said controlling means also including means for openingsaid inlet pipe valve means after said period; whereby the exhaust gasesflow through said housing from the inlet end of said inlet pipe to saidoutletting means.
 21. Muffler apparatus for reducing both sound andparticulates from exhaust gases from an engine, said apparatuscomprising:a muffler-filter device including a housing having an inlet,an outlet, and a fluid flow path leading from said inlet to said outlet,said housing containing a first reactive acoustic element, said housingalso containing means for filtering the particulates from the exhaustgases, said filtering means including a ceramic filter element, saiddevice including means for regenerating said ceramic filter element; amuffler including a second reactive acoustic element; first means forfluidly communicating between said engine and said muffler-filterdevice, said first communicating means including a first valve; secondmeans for fluidly communicating between said engine and said muffler,said second communicating means including a second valve; and means forcontrolling said regenerating means and said first and second valves,said controlling means positioning one of said first and second valvesopen and the others closed.
 22. Muffler apparatus for reducing the soundof exhaust gases from an engine, said apparatus comprising:first andsecond muffler devices, each of said first and second duffler deviceshaving a reactive attenuation chamber, said first muffler deviceincluding means for filtering particulates from the exhaust gases, saidfiltering means including a ceramic filter element; means forperiodically regenerating said filtering means, said regenerating meansincluding means for heating one end of said filter element and means forblowing combustion air through said heating means toward said filterelement; valve means for Controlling the flow of exhaust gases to saidfirst and second muffler devices; means for connecting said first andsecond muffler devices, said valve means and said engine in fluidcommunication so that said first and second muffler devices are in aparallel combination; and means for controlling said regenerating meansand said valve
 23. Apparatus in accordance with claim 22 wherein saidvalve means includes a three-way, three position valve, said valve insaid first position placing said engine in fluid communication with bothof said first and second muffler devices, said valve in said secondposition placing said engine in fluid communication with only said firstmuffler device, said valve in said third position placing said engine influid communication with only said second muffler device.
 24. Apparatusin accordance with claim 22 wherein said connecting means includes apipe from said engine splitting into a pair of legs, said valve meansincluding a two-way, two position valve in each leg of said pair of legsof said pipe.
 25. A method for making a particulate filter module, saidmodule including a ceramic filter element having opposite ends and aside region therebetween, said module including a housing formed from acylindrical metallic sheet which encloses the side region of the filterelement and has inwardly turned ends to retain said ilter elementtherebetween, said module further including a heat resistant materialbetween said filter element and said housing and sealing means betweensaid heat resistant material and said inwardly turned ends, said methodcomprising the steps of:wrapping the side region of said ceramic filterelement with said heat resistant material; slipping said wrapped ceramicfilter into said housing; placing said sealing means at ends of saidheat resistant material; and forming said inwardly turned ends on saidhousing to compress a portion of said sealing means between said ceramicfilter element and each of said inwardly turned ends of said housing.26. The method in accordance with claim 25 including prerolling ametallic sheet before slipping said wrapped ceramic filter into it andafter slipping said wrapped ceramic filter into said prerolled metallicsheet squeezing said rolled sheet to a predetermined cylindricaldimension and welding facing edge portions together.
 27. A method formaking a particulate filter module, said module including a ceramicfilter element having opposite ends and a side region therebetween, saidmodule including a cylindrical metallic housing enclosing the sideregion of the filter element and having inwardly turned ends to retainsaid filter element therebetween, said module further including anintumescent resistant material between said filter element and saidhousing and sealing means between said intumescent material and saidinwardly turned ends, said method comprising the steps of:wrapping theside region of said ceramic filter element with said intumescentmaterial; slipping said wrapped ceramic filter into said housing;placing said sealing means at ends of said intumescent material; formingsaid inwardly turned ends on said housing to compress a portion of saidsealing means between said ceramic filter element and each of saidinwardly turned ends of said housing; and heating said module so thatsaid intumescent material intumesces.